Wet spinning synthetic fibers



Oct. 30, 1962 J. H. SANDERS 3,

WET SPINNING SYNTHETIC FIBERS Filed NOV. 15, 1960 Me rer/ng Gaoe/ loam/0Dry .5 /re/c/7 Wash oa gu/an Ff/amen/ band/e fi o/n0 ere/1 6 #1 60// c//I a: 5 g

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Jo/v; M Sande/1s United States Patent tion of Delaware Filed Nov. 15,1960, Ser. No. 69,315 8 Claims. (Cl. 18-54) The present inventionresides in the field of synthetic textile fibers and contributes to theart of their manufacture. More precisely, it relates to a useful andadvantageous process for the continuous Wet spinning of manmade fibersthat are prepared by being coagulated from suitable spinning solutionsor equivalent compositions (such as spinnable dispersions) in aqueouscoagulating spin baths. The invention has particular reference to themanufacture of acrylonitrile polymer fibers which are fabricated fromfiber-forming acrylonitrile polymers that contain in the polymermolecule at least about 80 weight percent of polymerized acrylonitrile,especially polyacrylonitrile, which are wet spun in and with systemsthat are adapted to utilize aqueous coagulating liquids for the spinningoperation, such as systems wherein ethylene glycol, dimethyl formamide,dimethyl sulfoxide, butyrolactone and the like or the various aqueoussaline polyacrylonitrile-dissolving solvents are employed as spinningsolution solvents for the polymer and are also present innon-polymer-dissolving quantities in the aqueous coagulating liquid usedin the spin bath.

The ut-ile, known aqueous saline solvents for the various fiber-formingacrylonitrile polymers and polyacrylonitrile include zinc chloride, thevarious thiocyanates such as calcium, lithium bromide, salt mixtures ofthe so-called lyotropic series, and others recognized by the art, as hasbeen disclosed, among other places, in United States Letters PatentsNos. 2,140,921; 2,425,192; 2,648,592; 2,648,593; 2,648,646; 2,648,648;2,648,649; and 2,949,435. Advantageously, aqueous zinc chloridesolutions are used for the purpose.

The known methods of fiber-forming may generally be classified in threecategories; melt spinning, dry or evaporative spinning, and wetspinning. Briefly, melt spinning entails extruding a molten polymer andcoagulating the extruded filament by cooling with an inert gaseousmedium. In dry spinning, the fiber-forming material or polymer isdissolved in a suitable volatile solvent, and the resulting solution isextruded into a heated atmosphere wherein the solvent is evaporatedleaving a coagulated filament. In wet spinning, like dry spinning, thefiberforming polymer is dissolved in a suitable solvent (which is notnecessarily volatile) and the solution is extruded or spun into a liquidcoagulating or spinning bath which is a solvent for or miscible with thepolymer solvent but a non-solvent for the extruded polymer. Thus, thepolymer solvent is dissolved or leached out of the polymer leaving acoagulated polymeric filament.

in the prior known methods of wet spinning, the spinnerette is usuallyimmersed in a coagulating bath or placed just immediately preceding abath so that the extruded solution is contacted immediately withcoagulant upon emergence from the spinnerette face. In any event, anactual bath has always been employed for coagulating, that is, thesolution has been extruded into a confined volume of liquid. The shapeof the bath container has not been limited, taking on numerousgeometrical configurations from cube-like to cylindrical. Ordinarily,rectangular trough-like baths are employed with the upper surface of thebath exposed to the atmosphere. However, totally enclosed baths arefrequently encountered as in cylindrical chambers oftentimes used intube spinning. The direction of spinning has been vertically upward ordownward, horizontal or oblique so long as in the path of the spinningwas a confined coagulating bath.

The necessity to maintain a coagulating bath presents many processingand economic difliculties among which are: considerable floor space isrequired to accommodate the baths; the spinnerettes are usuallyinaccessible for observation and maintenance; means are required to movethe spinnerettes into and out of the baths such as having thespinnerette assemblies pivotally mounted, which in itself is costlyconstruction and presents leak sources; threading-up or start-up isparticularly difficult; large inventories of coagulating liquids areoften necessary; and, problems of adequate mixing and prevention ofStratification in the bath are prevalent due to concentration gradientsthat develop during spinning.

It is the chief aim and concern of this invention to provide awet-spinning process that will eliminate or minimize the above and otherdifficulties and at the same time provide a process that will assureproduction of fibers of consistently high quality. A particular objectof the invention is to provide a process of the indicated type andnature that would be peculiarly well adapted for utilization for and inthe prepartion of aerylonitrile polymer fibers, yarn, threads, towbundles and the like and related filamentary products using the highlyadvantageous salt spinning techniques with aqueoussystems, such as thosethat employ aqueous solutions of Zinc chloride or its saline equivalentsfor dissolution of the polymer into a spinning solution and forconstitution, in non-polymer-dissolving quantities, of the coagulatingliquid.

These objects and cognate benefits and advantages may be achievedreadily in the practice of the present invention whose process, incontinuous and uninterrupted sequence, comprises and entails extrudingor spinning into filamentary or the like form a spinning solution of asynthetic fiber-forming polymer dissolved in a watermiscible solvent forsaid polymer, said spinning solution being adapted to be coagulated inan aqueous solution of said solvent of non-polymer-dissolvingconcentration, said spinning solution being extruded through a suitablespinnerette or other extruding device vertically upward while applyingto the so-formed filaments at some point above the spinnerette face anaqueous coagulant, and allowing said coagulant to run down the filamentscounter-current to the run of the filaments to the spinnerette face,from which said non-polymer-dissolving solvent is withdrawn. Thus, thisinvention is based on the surprising discovery that a filament bundlecan be made to serve as its own coagulating bath.

Further features and advantages of the invention will be manifest in thefollowing description and specification, taken in connection with theaccompanying drawing, which schematically illustrates the invention.

Referring to the drawing, a spinning solution, a solution or dispersionof a polymeric fiber-forming material, is delivered from a pumping means(not shown) to a spinnerette which is positioned to spin or extrudeessentially vertically upward. Upon emerging from the spinnerette facethe freshly formed filaments are formed into a filament bundle and drawnover a godet serving to draw the filaments away from the spinnerette.The filaments may then be subjected to any number of subsequentprocessing treatments common to a wet spinning process, such as areillustrated, washing, stretching, and finally drying. The coagulation ofthe freshly extruded filament is provided by metering onto the filamentbundle a suitable coagulant at some point above the spinnerette face.

The composition of the coagulating liquid is preferably substantiallypure water or an aqueous solution comprising the same constituents asthe spinning solution solvents, but in non-polymer dissolvingconcentrations.

After application of the coagulant to the fiber bundle, the coagulant isallowed to travel down the filament bundle by gravity flow,counter-current to the direction of travel of the fiber bundle, to thespinnerette face and then to a suitable collecting pan positioned belowthe spinnerette. The spent or efiluent coagulant can then be Withdrawnfor further treatment.

The spinning solution may be a solution or spinnable dispersion of afiber-forming polymeric material that is capable of being coagulated inan aqueous coagulating spin bath. As has been indicated, whenacrylonitrile polymer, particularly polyacrylonitrile, fibers are beingmanufactured, zinc chloride may most advantageously be utiilzed as thesole, or at least the principal, saline solute in the spinning solventemployed for the polymer. In such instances, the aqueous solution ofzinc chloride in the spinning solution may advantageously be in aconcentration of from 55 to 65, preferably about 60 percent by weight,based on the weight of the aqueous solution.

The quantity and concentration of the coagulant applied and passedcountercurrent to the filaments should be sufficient, when such aqueousZinc chloride solvent spinning solutions are employed, so as to maintainthe concentration of zinc chloride in the zone immediately adjacent thespinnerette face at a non-polymer-dissolving coagulating concentrationof at least about percent by weight; advantageously from about to 50percent by weight, and preferably between about and percent by weight.In such aqueous zinc chloride systems for acrylonitrile polymers,wherein the freshly wet spun polymer is generally obtained in an aquagelform, it is generally desirable for the spinning solution that isextruded to contain between about 4 and 20 percent by weight ofdissolved polymer; more advantageously from about 6 to 15 percent byweight of dissolved polymer; and preferably, particlularly whenpolyacrylonitrile fibers are being manufactured, from about 8.5 to 11.5percent by weight of fiber-forming polymeric solids in the spinningsolution.

As the coagulant travels down the fiber bundle it will become enrichedwith the spinning solvent as the fibers are leached or washed free ofthe solvent. It is thus apparent that the concentration and point ofapplication of the coagulant must be gaged so that polymer-dissolvingconcentrations in the coagulant are nto attained during the down-flowcontact of the coagulant with the filaments.

Aqueous zinc chloride spinning solutions of fiber-form- 1 ingacrylonitrile polymers are beneficially extruded at a spinningtemperature of from O to C.; preferably from about 10 to 30 G, into anaqueous Zinc chloride coagulating liquid that is maintained at acoagulating temperature of from 0 to 30 C.; preferably from about 10 to20" C. Under the indicated conditions, the amount and concentration ofcoagulant that is required to effect a suitable coagulation in the areaof the spinnerette face can be determined by simple material balance,taking into account the quantity per unit time of spinning solutionbeing extruded and the amount of water being withdrawn from the liquidby entrapment and entrainment in the freshly wet spun and washed aquagelfilaments. Similarly, a desirable point of application can bedetermined. Thoroughly washed acrylonitrile polymer aquagel fibers,incidentally, are usually found to contain not more than 5 /2 parts byweight of water (including residual extrinsic or exterior waterassociated therewith) for each part by weight of dry polymer therein.More frequently, Washed acrylonitrile polymer aquagel fibers are foundto contain from about 2 and usually from about 3 to 4 parts by weight ofwater for each part by weight of polymer.

When practicing the present invention, it is usually advantageous toposition the take-away godet over the spinnerette so that the travel ofthe filament bundle is vertically upward. This allows the coagulant toflow down around and within the filament bundle without any inordinatechanneling due to one side of the bundle being lower than another.However, travel at slight inclinations from the vertical may in someinstances be satisfactory. Ordinarily, the coagulant flows down into ashallow pool which is inherently maintained on the face of thespinnerette and then over the side to a collecting receptacle.Incidentally, no inventory of spent coagulant need be maintained belowthe spinnerette. Instead, the coagulant may be withdrawn at the samerate it overflows the spinnerette face.

The size of the spinnerette and the number of individual orifices in thespinnerette are not critical. For instance, spinnerettes of round,rectangular, square, etc. shapes having face areas up to 25 squareinches or so and from a few hundred to several thousand orifices may beemployed. Of course, a plurality of spinnerettes may be operatedsimultaneously but when so doing it is preferable to individually applycoagulant to each filament bundle. A common header system can beemployed so that the feed rate of coagulant is the same to all bundles,or the coagulant can be individually metered to each bundle. A commontake-away godet may serve several filament bundles simultaneously.

Several means of administering the coagulant to the fiber bundle arepossible. It may be administered by a running stream, drop-wise,spraying, padding, etc. Advantageously, the coagulant is applied to thefilaments at the point at which they make contact with the takeawaygodet or immediately below the godet. The bundle at this point occupiesthe least volume and problems of distribution of the coagulant on thebundle are minimized. If application is desired nearer the spinnerette asuitable distributor may need to be employed, such as a tube encirclingthe tow and perforated so that coagulant is sprayed inwardly on thebundle.

The height of the take-away godet above the spinnerette is beneficiallyfrom about two to five feet, but the exact height is best determined foreach particular set of spinning conditions being practiced. For instancethe height will be somewhat dependent on filament composition anddenier. The speed of the godet is preferably set to coincide with thespinning speed or slightly higher so that a slight stretch is impartedto the filaments; for example, a stretch of 1:1.4 may be beneficiallygiven the freshly formed filaments between the spinnerette and thegodet.

Starting-up the spinning operation according to the invention is arelatively simple procedure. Usual operation is to start the spinningpump and extrude a mass of spinning solution through the spinnerettewhich is then coagulated by pouring water on the exuding mass. Thecoagulated mass is then used as a leader and is drawn away by hand asthe filaments are formed behind it, laced over the godet and throughsubsequent treating operations.

As another modification of the invention, saturated steam may be sprayedon the filament bundle and caused to condense serving as the coagulant.Certain conditioning effects can be obtained by such treatment.Additionally, the coagulant may be metered onto the filament bundle atmore than one elevation, and differing concentrations may be employed ateach elevation. The application of water to the filaments may be soadapted, such as at the upper extremity of vertical climb of thefilaments, that filaments essentially free of residual spinning solventare obtained.

After spinning and coagulating, the freshly wet spun filaments may besubsequently handled and treated in any desired or necessary manner forpurposes of converting them to a finished fiber product. Thus, they maybe stretched or otherwise treated for purpose of heat treating orrelaxing the fibers in any desired way or they may be subjected toadditional treatments of any appropriate nature, including applicationof finishes, lubricants and the like or imposition of crimp prior tobeing dried and finally collected as completely manufactured products.

The invention will be further illustrated with the following example inWhich all parts and percentages are by weight unless otherwisespecified.

Example 1 A spinning solution was prepared comprised ofpolyacrylonitrile with an average molecular weight between about 30 and35 thousand dissolved in an aqueous 60 percent by weight solution ofzinc chloride. The total polymer solids in the spinning solution wereabout percent by weight, based on the weight of the solution.

The solution was pumped through a spinnerette (500 hole, 8 mils perhole), positioned to spin in a vertically upward direction, at about 40grams per minute at 20 C. At the start of the run, the spinning solutionwas coagulated at the spinnerette face by running water at the face sothat a bulky mass of coagulated solution was obtained. This mass wasused as a leader for threading up the filament bundle. As the mass wasdrawn upward from the spinnerette, an open stream of water was appliedbeneath the mass so that individual filaments were formed at thespinnerette face and extended up to the bulky coagulated mass.

After the filament bundle was laced over a take-away godet, roomtemperature water was metered onto the filaments adjacent their initialpoint of contact with the godet, and the water was allowed to run downthe fiber bundle, without any additional confining or controlling means,to the spinnerette face and into a collecting pan beneath thespinnerette. The distance from the spinnerette face to the godet wasabout 34 inches. The efiluent coagulant from the collecting pan had aconcentration of about 26 percent ZnCl Continuous spinning of fibers wasmaintained from a feed rate of 40 grams per minute of spinning solutionand from metening substantially pure water to the fiber bundle as aboveat about 80 grams per minute. The takeup godet was driven at 5 rpm.which corresponds to about 4.7 ft./min. After passing over the take-upgodet the fibers were washed and hot-stretched about 8:1, and finallydried at about 140 C. for 7 minutes.

The resulting fibers were surprisingly uniform, had an excellent whitecoloring and had the following physical properties:

Yield 0.42

Since certain other modifications and ramifications of this inventioncan be entered into without departing from its intended spirit andscope, the invention is intended to be definitive in the hereto appendedclaims without unnecessary limitation to or by the foregoingspecification and description.

What is claimed is:

1. Method for continuously Wet spinning synthetic textile fibers whichcomprises forming a water-coagulable spinning solution of a syntheticfiber-forming polymer in a water-miscible solvent for said polymer,extruding said spinning solution through a filament shaping device in asubstantially vertical upward direction, applying an aqueous coagulantto the so-formed filaments at a distance above said filament-formingdevice and allowing said aqueous coagulant to flow down said filamentsin an unconfined manner counter-current to the run of said filaments tosaid filament-forming device.

2. The method of claim 1, wherein said aqueous coagulant is applied tosaid filaments adjacent the point of contact of said filaments with agodet positioned vertically above said filament-forming device.

3. The method of claim 1, wherein said aqueous coagulant is essentiallypure water.

4. The method of claim 1, wherein said spinning solution is extrudedthrough a filament shaping device in an absolutely vertical upwarddirection.

5. The method of claim 1, wherein said spinning solution is comprised ofa fiber-forming acrylonitrile polymer containing in the polymer moleculeat least about 80 percent by weight of acrylonitrile dissolved in awater miscible solvent therefor.

6. A method in accordance with the method set forth in claim 4, whereinsaid solvent is an aqueous polyacrylonitrile-dissolving saline solution.

7. A method in accordance with the method set forth in claim 5, whereinsaid aqueous saline solution is a solution of zinc chloride in waterthat contains from to percent by weight of dissolved zinc chloride,based on the weight of the solution.

8. The method of claim 1 and including, in combination therewith and inaddition thereto, the subsequent step of withdrawing said aqueouscoagulant.

References Cited in the file of this patent UNITED STATES PATENTS2,140,921 Rein Dec. 20, 1938 2,577,763 HoXie Dec. 11, 1951 3,006,027Hildebrandt et al Oct. 31, 1961

1. METHOD FOR CONTINUOUSLY WET SPINNING SYNTHETIC TEXTILE FIBERS WHICHCOMPRISES FORMING A WATER-COAGULABLE SPINNING SOLUTION OF A SYNTHETICFIBER-FORMING POLYMER IN A